Pseudo-zeroth-order reactions

Differential temperature method. A differential method has been applied to a study of the iodination of acetone, a pseudo-zeroth-order reaction when [(CHj)2CO] [I2].26 It allows the determination of AW to much higher accuracy than otherwise. The reaction rate is expressed mathematically as... 

Elementary reaction 2H20(aq) H30+(aq)+ OH (aq) (Reaction l-9f) is a zeroth-order reaction (or pseudo-zeroth-order reaction) ... 

The results of this analysis are illustrated in Figure 27. Several interesting observations may be made about these data. Ffrst, the rate of increase in Xac Is approximately constant as a function of time, thereby implying a pseudo-zeroth-order reaction rate law for the formation of the active complex. Secondly, xac,0 is shown to be a function of the stoichiometric ratio, R, based on a linear extrapolation of Xac to... 

Probably no reaction is truly zeroth-order. However, one might employ a very high concentration of the species on which the rate does depend to create pseudo-zeroth-order conditions. If the rate is independent of the limiting reagent, A, it is given by... 

If the rate of phase transfer is much slower than the rate of reaction, then the reaction will be mass transport limited-typically pseudo-zeroth order, unless the availability of the nucleophile becomes significantly depleted over the course... 

A semiempMcal rate law has been developed which describes the epoi -phenol reaction as catalyzed by triphenylphosphine. It involves a pseudo-zeroth-order activated complex formation step and a first-order propagation step. The activated complex appears to exist in an equihbrium state. The activation energies of the initiation and propagation reactions are similar, vdiich suggests that these reactions share similar rate-limiting steps. 

Distinguish between zeroth-order, first-order, second-order, and pseudo-first-order reactions. 

Reactions may also be classified on a kinetic basis by reaction order, which may be zeroth-order, first-order, second-order, third-order, or pseudo-first-order, contingent on how the reaction rate is affected by the concentration of the reactants. The rate equation for the reaction A — P may be written as... 

Pseudo-Order Reactions As mentioned above, complex reactions can often be expressed by the simple equations of zeroth-, first-, or second-order elementary reactions under certain conditions. For example, the dissolution of many minerals at conditions close to equilibrium is a strong function of the free energy of the reaction (Lasaga, 1998, 7.10), but far from equilibrium the rate becomes nearly independent of the free energy of reaction. In other words, the rate of dissolution will be virtually constant under these conditions, or pseudo-first-order. 

In spherical coordinates, the dimensional mass transfer equation with radial diffusion and first-order irreversible chemical reaction exhibits an analytical solution for the molar density profile of reactant A. If the kinetics are not zeroth-order or first-order, then the methodology exists to find the best pseudo-first-order rate constant to match the actual rate law and obtain an approximate analytical solution. The concentration profile of reactant A in the liquid phase must satisfy... 

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